Dart SHP 427 Small Block Engine - The Anti LS Part 2

Like any good cliff-hanger, when we left you last month, our Anti-LS small-block engine was well underway at Dart Machinery. But would we be able to do what we set out to? Could we build a Gen I small-block Chevy that could run with the new favored-son LS engines? Would it be streetable? Dependable? Would Charlie finally ask Diane to marry him? Wait, wrong soap opera.

2/24

We reconvened with Jack McInnis, Tony McAfee, and Jeff Lake at Dart to finish the build and dyno test the small-block to see if we had a winner, or wishful thinking. Last month, the crew at Dart machined and assembled a stout SHP short-block as the foundation for our anti-LS engine. Using the company’s iron SHP block with a 4.000-inch bore, they tossed in a 3.750-inch Eagle crank, CompStar steel H-beam rods, Mahle flat-top pistons and a COMP Cams solid-roller camshaft.

With 427 ci in the short-block and a camshaft worthy of its solid roller construction, this engine needed a pair of cylinder heads that could deliver a healthy volume of air/fuel mixture. We had two additional requirements for the cylinder heads. First, they needed to be a traditional 23-degree design with stock valve and port locations. That way a regular intake manifold and headers would bolt up; in fact, the whole exhaust system that is already in our Laguna should reattach nicely. Second, they had to flow like tax dollars into the national debt right out of the box. By avoiding hand porting, we’re building an engine that you can duplicate exactly with off-the-shelf parts. You can thank us later. The Dart Pro 1 CNC heads were exactly what we were looking for. They are fully CNC machined for precision, and the intake ports are a massive 227 cc. At .700-inch lift, the intakes will flow 309 cfm, and we’re in that ballpark at .688 inch of lift at the valve with our COMP Cams roller camshaft and 1.6:1 rocker arms. The exhaust side is matched proportionally to the intake, with 226 cfm at .700-inch lift.

3/24 We detailed the components and assembly in this Dart SHP 427 short-block last month. In case you missed that, the CliffsNotes version is that it’s an all-new cast-iron block with clearance for a 3.750-inch stroke with steel rods and up to a 4.125-inch unfinished bore. Ours has a 4-inch stroke Eagle 4340 forged steel crank, CompStar H-beam steel rods, and Mahle forged flat-top pistons.

For the most part, the valvetrain in this 427 is made up of COMP Cams matched components. We like this approach because the cam manufacturer generally has a good matched set of valvesprings, and all of the related parts such as lifters and pushrods are designed to play nicely with each other. The only valvetrain parts that are not from COMP are the 2.08/1.60-inch valves and adjustable guideplates, which all came from Dart.

We introduced you to our custom bumpstick last month, but the specs merit repeating here. The intake lobes sport 259 degrees of duration at .050-inch lift while the exhaust side has 268 degrees. Lobe separation is 108 degrees, and lift on both lobes is .430 inch, which gives us a gross lift of .688 inch with the COMP Cams Ultra Pro Magnum 1.6 rocker arms. This camshaft is aggressive for the street by most people’s standards, but this engine isn’t meant to be a docile, smooth idle, high-vacuum and otherwise yawn-inspiring small-block. We’re pushing the envelope of streetable power and with that comes a higher, rougher idle, and getting intimate with the fine line of durability. This engine won’t require a ton of maintenance, but checking the valve lash twice a year will let you know if any of your valvetrain parts are wearing and need attention.

Enough with the disclaimers and onward to making the kind of power that every small-block Chevy owner dreams of. With the cylinder heads and valvetrain selected, it was time to pick out some induction components. The perfect match for the Dart Pro 1 CNC heads is the Dart single-plane intake. This intake features extended runner dividers inside the plenum to equalize port length. They are also radiused with the angled runners to move massive amounts of air/fuel mixture to the individual intake ports of the heads. To top off the intake, we used a brand-new Holley Ultra HP carburetor. This latest version of the Holley carb features countless new features, which will make tuning for the street and various types of racing we plan on doing easier than ever. Some of our favorite features are the aluminum construction that makes the carb about 30 percent lighter than a traditional 4150-style double pumper, internal baffles in the fuel bowl that will help control fuel slosh, adjustable secondary link, billet metering blocks with integrated pry-point, and the ultracool Hard Core Gray hard coat anodized finish. These may become our new favorite carbs. With the engine size, cam specs, and head volume, there was debate on whether an 850- or 950-cfm carb would make the most power on the dyno, so we tested both.

7/24We chose a TCI Rattler 2000 damper for this engine build. The Rattler is designed to absorb torsional vibration with an internal pendulum absorber. It doesn’t have any components that will wear or age, so it requires no maintenance or periodic rebuilding. It’s also one of the lightest dampers available.

The last thing we needed before we could light the fire in this thing was an igniter. We love the simplicity of an HEI, and having all of our ignition components under a single cap, so we called Performance Distributors and Steve Davis recommended that we try his latest distributor. It has all the features of his standard HEI system, but has a unique instant timing knob that lets you adjust the timing by turning the knob, and a slip collar so it can be used with a variety of deck heights and intake manifold types. These new features add about $210 to the price of a regular Performance Distributor HEI, so consider that when you review the “Where the Money Went” sidebar.

8/24At the rear of the engine, we will use a TCI flexplate to fit our automatic trans in the Laguna. This steel flexplate is made in the USA and SFI spec’d, which will be important for us when we hit the racetrack. The Dart SHP small-block Chevy engines are all internally balanced, making the selection of dampers and flexplates/flywheels that can be used very generous.

With that, it was time to shelf the bench racing, put spark to fuel, and watch the dyno needles dance to see what this big-inch small-block could produce. With its first breath, this engine seemed eager to prove its worth. Check out “Let’s Rock!” to read about the results we found during our dyno session.

Let’s Rock!

Enough talk about the parts, what’s all of this worth in terms of pump-gas power? We strapped the big-inch small-block SHP 427 to Dart’s dyno and made a dozen pulls. From the first time spark hit fuel in the cylinders, we realized just how potent this engine was. It sounds plain angry, even as it idles down to about 900 rpm.

9/24Before we could bolt the oil pan on, the oil pan gaskets needed to be cut. Using a permanent marker, Jeff noted the location of each of the rod-clearance notches in the pan rail. The guys at Dart have a really cool tool for cleaning cutting sections of gasket away, but we can manage with a razor blade and a flat surface.

Our goal was to crest the 600hp mark with a Gen I motor that had enough durability and manners to be driven on the street. The Dart SHP 427 bettered that goal on the first pass. By the end of the day, we had captured an extremely respectful 627 hp with an equally impressive 561 lb-ft of torque! That’ll get your attention.

We tried both an 850-cfm Holley Ultra HP carburetor and a 950 version in case the engine wanted even more fuel at the top end. The power numbers were pretty similar throughout the powerband with both carbs, but ultimately the 850 made more power, confirming that it’s the right size for this combination.

With a peak horsepower of 627, we surpassed our goal for this Gen I motor, proving that an engine doesn’t have to start with the letters “LS” to make serious power. We can pass this Chevy-orange beast off as a 305 or 350, or proudly proclaim its true displacement of 427 ci. And the best part is that it will bolt to our existing accessories, exhaust, and transmission.